lecture 1 Flashcards
what are the functions of the stomach?
- store and liquefy food
- liquefaction (acid, pepsin, muscle contractions)
what is the anatomy of the stomach?
- oesophagus (enters top)
- sphincter (
- greater and lesser curvature (corpus)
- antrum (bottom part)
- pylorus (better sphincter)
what does the sphincter do?
- controls movement of fluid
- air escapes through forming burp
what is the function of pylorus?
- allows fluid/material to empty out into duodenum
- better sphincter than cardiac sphincter
what happens to musculature from top to bottom?
- increases
- more muscular in antrum
what are the layers of stomach wall?
- outside = connective tissue, muscle, autonomic nerve plexus
- middle = submucosa (lots of blood supply)
- inner = gastric glands, epithelium, lymph nodes
when are goblet cells found in the stomach?
- if pre cancerous changes occur (only found when in diseased state)
what is the structure of the gastric gland?
- top = mucus secreting neck cells
- middle = stem cells, parietal and chief cells
- bottom (base) = neuroendocrine cells
where are gastric glands found?
- gastric pits
what do mucus secreting neck cells migrate to form?
- epithelium of surface of stomach
- secrete mucous
what are neuroendocrine cells?
- are nerve cells that make hormones
what neuroendocrine cells are present in base of glands?
- enterochromaffin
- enterochromaffin like cells
- D cells
(change function based on location in gland)
what do enterochromaffin cells secrete?
- serotonin
what do enterochromaffin like cells (ECL) secrete?
- histamine (control of acid secretion)
what do D cells produce?
- somatostatin
what do G cells secrete?
- gastrin (control of acid secretion)
where is acid secretion happening?
- top of stomach
- antrum doesnt secrete
- pepsinogen secreted all over
what do surface epithelial cells secrete?
- mucus
- forms continuous mucus layer
- first line of defence against gastric juice
does the continuous layer of mucus extend into oesophagus?
- no
- stomach has columnar epithelium
- oesophagus is squamous epithelium (dead cells at surface so no need to protect- don’t need layer over dead cells) - doesn’t have a mucus layer
what is the structure of gastric mucus bilayer?
- 2 layers within the mucus layer
(protection for stomach)
what are the two layers?
- shear compliant layer
- shear resistant layer
what is the shear compliant layer (on top)?
- gel but can be converted to viscous liquid
- becomes lubricant
- has variable thickness
what is the shear resistant layer?
- remains intact
- 150 um thick
what is the purpose of the layers?
- opposes the degradation from pepsin
how is the layer maintained?
- secreted from epithelial cells underneath the layer
- secretion balances degradation to maintain the layers (dynamic balance)
what is the composition of gastric juice?
- mucus (salary and gastric)
- lipases
- pepsins
- urea
- intrinsic factor and haptocorrin
- H20
- ions
- salivary amylase
what is the purpose of the mucus in gastric juice?
- lubricant so food can pass down oesophagus
what is the purpose of the lipase in gastric juice?
- aids in fat digestion
what is the function of salivary acid in the gastric juice?
- not active
- gastric juice shouldn’t be pH7 which is optimal for amylase
what is gastric lipase pH activity?
- between pH 2.5 and around 5-6
how does pH change?
- food buffers gastric juice
- allows pH to increase to around 5
how does acid secretion occur?
- when stimulated (by histamine and gastrin), H2 receptors bind
- hydrogen potassium pumps trafficked to membrane when stimulus present (require ATP)
- tubulo cysterni migrate along actin cytoskeleton to membrane (supported by actin scaffold)
- secrete acid
what is the tubulo cysterni?
- series of plates where pumps are stored
what happens once stimulus its removed?
- dissolving of actin scaffold
- pumps travel back to tubulo cysterni
what is the treatment for gastric ulcers?
- H2 antagonists (stops the acid secretion)
- proton pump inhibitors (PPIs)
what is the function of carbonic anhydrase?
- forms bicarbonate that dissociates into hydrogen ions and co2
what happens to the dissociated bicarbonate?
- transferred out across basolateral membrane
- chloride enters
- hydrogen pumped out
- hydrochloric acid forms
how is the HCl produced?
- chloride channel present
- exchange of hydrogen ions for potassium (brings potassium in)
- potassium channel to allow exit
what is the H+/K+ATPase?
- intracellularly = app activator, catalytic site
- lots of transmembrane sections (needs conformational changes)
- mostly alpha subunit, 1 beta
how does the ATPase bind with PPI?
- forms disulphide bridge with present cystine
what happens when you stop taking PPIs?
- surge of acid secretion
- need maintenance dose
